If a researcher selected five schools at random and then interviewed each of the teachers in those five schools, the researcher used

Selecting five schools at random and studying every teacher in them is cluster random sampling.

Simple random sampling would draw individual teachers directly, not whole schools.

Stratified random sampling would divide teachers into strata and sample within each stratum.

Convenience sampling would take the nearest available teachers with no random step.

Each chosen school is a cluster whose members are all included once the cluster is picked.

Clusters are naturally occurring groups, making this design cheaper for field surveys.